Tobacco smoke filter material and process for the preparation thereof

ABSTRACT

Disclosed are materials and compositions effective for the selective removal of gaseous aldehydes from tobacco smoke. The materials and compositions comprise tobacco smoke filters comprising a fibrous material or fibers of a polymeric material containing covalently-bonded acetoacetoxy residues. The fibrous material or fibers are capable of reacting with and removing aldehydes present in tobacco smoke. Also disclosed are processes for the preparation of fibrous materials and fibers of a polymeric material containing covalently-bonded acetoacetoxy residues and methods for the removal of a gaseous aldehyde from tobacco smoke by contacting tobacco smoke with the aforesaid fibrous materials or fibers containing covalently-bonded acetoacetoxy residues.

FIELD OF THE INVENTION

This invention relates to materials and compositions which are effective for the selective removal of gaseous aldehydes from tobacco smoke. More specifically, this invention pertains to a tobacco smoke filter comprising a fibrous material or fibers of a polymeric material containing covalently-bonded acetoacetoxy residues. The fibrous material or fibers are capable of reacting with and removing aldehydes present in tobacco smoke. This invention also pertains to the preparation of fibrous materials and fibers of a polymeric material containing covalently-bonded acetoacetoxy residues. This invention further relates to a method for the removal of a gaseous aldehyde from tobacco smoke by contacting tobacco smoke with the aforesaid fibrous materials or fibers containing covalently-bonded acetoacetoxy residues.

BACKGROUND OF THE INVENTION

Tobacco smoke resulting from tobacco combustion contains numerous gaseous molecules and particulates. These gaseous molecules are responsible for both the pleasure and the health risks experienced by users of tobacco products. Among the many molecules produced by tobacco combustion or vaporization are nicotine, carbon monoxide, ammonia, aldehydes such as formaldehyde, acetaldehyde, and acrolein, and compounds from any added flavoring materials. Tobacco smoke filters are utilized to remove undesirable gases and particulate materials from tobacco smoke while retaining the flavor and taste essential for the enjoyment of smoking. The selective removal of gaseous molecules from tobacco smoke stream therefore is required for an active filtration material to be acceptable. Active materials such as activated carbon, silica gel, alumina, and zeolites commonly used for the removal of gaseous contaminates are not particularly suitable for this purpose. Although such materials may remove undesirable gaseous molecules, they also adsorb molecules considered necessary for acceptable tobacco smoke flavor. Moreover, the adsorption by these porous materials is not considered effective since the molecules are only physically bound to the surface and not chemically reacted. In addition to selective adsorption and chemical adsorption, other desired properties for active materials to be used in a tobacco smoke filter are light weight, low cost, stable in air, low pressure drop, safe to handle, and ease of fabrication.

U.S. Pat. No. 6,595,218 discloses a tobacco smoke filter comprising a reagent consisting essentially of aminoethylaminopropylsilyl silica gel or aminoethylamino-ethylamino-propylsilyl silica gel wherein the reagent chemically reacts with and removes gaseous components such as aldehydes of a tobacco smoke stream. U.S. Pat. No. 6,481,442 discloses a smoking article comprising a wrapper and a selective filter element having at least one carrier and a polyaniline having a plurality of moieties selected from the group consisting of an amino group, an imino group, a hydrazide group, a hydrazone group, a semicarbazide group and combinations thereof capable of a nucleophilic attack of carbonyl-containing combustion products of the smoking article. Optionally, a spacer having a composition of —CO—[CH₂]_(n)—CO— with n having a value from 1 to 4 or greater than 4, may be used to attach said active moieties containing amino groups to the carrier. The spacer is used for the purpose of extending out the chemically active amino moieties from the carrier.

U.S. Pat. No. 4,182,743 discloses a gas-permeable substrate, particularly adapted for the selective removal of aldehydes from gases, comprising a granular containing concentrated hydrogen peroxide, water and a hydrophilic stabilizer for said hydrogen peroxide. U.S. Pat. No. 4,753,250 discloses a process for producing cigarette filters comprising a compound containing L-ascorbic acid to react with and remove aldehydes. U.S. Pat. Re. 28,858 discloses an improved tobacco smoke filter material comprising a porous particulate carrier impregnated with polyethylene-imine for the removal of volatile smoke acids and aldehydes. U.S. Pat. No. 5,009,239 also describes the removal of aldehydes using polyethyleneimine as the active component in a cigarette filter. For the same purpose, an aminobenzene acid salt is used in U.S. Pat. No. 5,603,927 and an organic salt of mercapto-alkane-sulphonate is used in U.S. Pat. No. 4,532,947. U.S. Pat. No. 5,206,204 discloses an adsorbent for lower aldehydes which comprises a saturated cyclic secondary amine and a halogenide of an alkali metal or alkaline earth metal supported on a porous carrier.

Various technologies have been cited in the prior art for the purpose of removing airborne formaldehyde. U.S. Pat. No. 5,352,274 discloses air filtration utilizing a plurality of corrugated base sheets which are stacked or nestled and which have entrapped carbon dust for adsorption of impurities such as formaldehyde, acetaldehyde, and acrolein. The corrugated structure provides very little pressure drop as the air passes through available channels and large, powerful fans are not necessary to move air therethrough. This technology provides a method to adsorb formaldehyde molecules physically but not by chemically reaction. U.S. Pat. No. 5,830,414 discloses an air cleaning filter comprising activated carbon fibers in the form of a web supporting at least one kind of chemical reagent selected from the group consisting of (a) an alkali agent selected from a hydroxide or carbonate of an alkali metal, (b) an acidifying agent selected from acid aluminum phosphate or phosphoric acid, and (c) an oxidizing agent composed of active manganese dioxide resulting from an alkali permanganate and an alkali iodate. U.S. Pat. No. 5,830,414 discloses the treatment of carbon fibers with an active small molecule such as a strong acid, strong base, or strong oxidizing agent. These chemicals can only be used to treat fibers having high chemical resistances such as activated carbon fibers. Further, fibers thus treated are potentially hazardous to handle.

U.S. Pat. No. 4,517,111 provides a composition comprising a permanganate salt adsorbed onto a solid alkaline support useful for irreversibly removing formaldehyde from air. The composition can be employed in molded, pellet, particle, or powder form as, for example, in a respirator filter cartridge. The application of this technology is limited to the solid forms as stated. U.S. Pat. No. 4,892,719 discloses a method of reducing the indoor air concentration of aldehydes by coating a porous support filter with a water soluble polymeric amine such as polyethyleneimine, polyallylamine, or polyvinylamine. The coating is further plasticized with a low volatile liquid such as glycerol in order to extend the useful life of the coating. This technology has a deficiency in that the reactive component, i.e., an amine, may be consumed by carbon dioxide present in air. The description of the reaction of carbon dioxide with amine adsorbents may be found in Int. J. Environmental Technology and Management, Vol. 4, Nos 1/ 2, 2004, p. 82. Furthermore, the reaction product of said polyamine and formaldehyde has the same end group as has urea-formaldehyde and, as a result, over time will undergo the same degradation to release formaldehyde.

It is known that compounds having active methylene groups are capable of reacting with formaldehyde. JP 57,032,729 described a method for removal of residual formaldehyde in microcapsule dispersion by adding a compound having an active methylene group such as methyl acetoacetate, ethyl acetoacetate, or diethyl malonate. Active methylene compounds also have been used as formaldehyde scavengers in the textile industry to reduce the amount of formaldehyde released from durable press-treated fabrics as described in Textile Chemist and Colorist, Vol. 16, No. 12, p. 33, December 1984 (published by the American Association of Textile Chemists and Colorists). Such a compound is added to finishing formulations of the fabrics to react with formaldehyde released from urea-formaldehyde resins used for cellulose crosslinking. Dimethyl 1,3-acetonedicarboxylate having two highly activated methylene groups was found to be most effective.

U.S. Pat. No. 5,160,503 discloses a water-soluble blend composition for scavenging formaldehyde in textile fabrics. The composition consists of a substituted or unsubstituted polyhydric alcohol such as diethylene glycol and an active methylene compound selected from the group consisting of dialkyl malonates and alkyl acetoacetates. U.S. Pat. Nos. 5,194,674; 5,268,502; and 5,446,195 disclose water-soluble compositions prepared by reacting a glycol or polyether with an acetoacetate or malonate that may be used as formaldehyde scavengers in the fabric finishing formulations. Again, in these references, liquid reaction media are required for the effective removal of formaldehyde. Formaldehyde scavengers containing active methylene hydrogens also may be added to coating compositions containing urea/formaldehyde or melamine/formaldehyde resin to reduce formaldehyde concentration. U.S. Pat. No. 5,795,933 discloses a waterborne coating compositions comprising a formaldehyde-containing resin and a formaldehyde scavenger containing active methylene hydrogen with a pKa of about 5 to 13.

The reaction of acetoacetate-functional polymers with formaldehyde also has been disclosed in the prior art. JP 58,059,263 describes a curable polymer composition consisting of a water soluble polymer, a water soluble polymer having an acetoacetate group such as acetoacetylated polyvinyl alcohol resin, and a crosslinking agent capable of reacting with the acetoacetate group such as formaldehyde or glyoxal. U.S. Pat. No. 5,767,199 discloses an air-curable composition containing an acetoacetate functional polymer and an end-blocked polyformaldehyde chain. According to the patent, the composition is stable to reaction until the formaldehyde is released from the polyformaldehyde chain. These references relate to either the utilization of active methylene compounds to remove formaldehyde in a liquid mixture or to suppress formaldehyde emission by mixing a formaldehyde scavenger with formaldehyde-containing resins. None of the references pertain to air filter applications.

U.S. Pat. No. 3,227,164 describes a tobacco smoke filter comprising a plasticizer bonding agent selected from the group consisting of the alkylene glycol, polyalkylene glycol, and glycerol esters of acetoacetic acid. This reference discloses that such a tobacco smoke filter is effective in removing phenol and other undesirable toxic metal ions such as nickel, cobalt, etc.; however, it does not disclose aldehydes removal.

The preparation of cellulose esters having acetoacetate functionality is known. U.S. Pat. No. 2,521,897 discloses the preparation of esters of acetoacetic acid by reacting a partially esterified cellulose with diketene in the presence of a tertiary organic base. U.S. Pat. No. 5,292,877 discloses water soluble cellulose acetoacetates prepared by contacting a cellulose material with diketene, an alkyl acetoacetate, 2,2,6-trimethyl-4H-1,3-dioxin-4-one or a mixture thereof in a solvent system comprising lithium chloride plus a carboxamide. U.S. Pat. No. 5,770,726 discloses a process for preparing a cellulose acetoacetate by contacting cellulose in a carboxylic acid diluent with an acetylating compound, an acetoacetylating compound selected from the group consisting of diketene, an alkyl acetoacetate, and 2,2,6-trimethyl-4H-1,3-dioxin-4-one, and a mineral acid catalyst. In these two references, the reactions are carried out in a homogeneous mixture by dissolving cellulose pulp in an organic solvent. GB Patent 940,954 discloses an improved dyeing process for cellulosic fibrous materials by pre-treating the fibers with diketene in a solvent such as benzene before dyeing. The patent, however, does not disclose or characterize the product composition after the treatment with diketene.

BRIEF SUMMARY OF THE INVENTION

We have found that gaseous aldehydes such as formaldehyde, acetaldehyde and acrolein may be removed selectively from tobacco smoke by contacting tobacco smoke containing one or more aldehydes with a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues. Thus, one embodiment of the present invention is a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues. A second embodiment is a method of removing a gaseous aldehyde from tobacco smoke by contacting tobacco smoke containing one or more aldehydes with a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues. A third embodiment in the invention is a smoking article comprising a first section comprising burnable tobacco and a second filter plug section comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues. The filter element permanently removes aldehydes from tobacco smoke. The fibrous filter element normally is in the form of a generally cylindrical filter affixed to or comprising a portion of a cigarette.

A fourth embodiment of our invention pertains to a method or process for the preparation of a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues which comprises contacting a fibrous material constructed of or comprising a reactant polymer containing hydroxyl groups with gaseous diketene.

DETAILED DESCRIPTION OF THE INVENTION

Examples of gaseous aldehydes which may be removed in accordance with the present invention include formaldehyde, acetaldehyde, acrolein, propanal, butanal, crotonaldehyde and other gaseous aldehydes present in tobacco smoke. Although the description of this invention is directed to the removal of aldehydes from tobacco smoke, the removal of other carbonyl compounds such as ketones capable of reacting with acetoacetate residues is within the scope of this invention.

The fibrous filter element of the present invention comprises fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues, i.e., acetoacetyl groups bonded to the polymeric material. Examples of the polymeric materials include cotton, regenerated cellulose (viscose or rayon), cellulose esters, polyesters, polyacrylates, polyurethanes, polyvinyl alcohols and epoxy polymers. Such fibrous substrates may be produced by conventional techniques such as solution spinning, melt spinning and melt blowing. The fibrous material or fibers may have various cross-section shapes and thicknesses, e.g., having a denier per filament of about 1 to 20, more typically about 2 to 8. The fibrous tobacco smoke filters may comprise various components used to construct tobacco smoke filters. Examples of filter components of tobacco smoke filters include cellulose acetate-based fiber tow, fiber-to-fiber bonding agents such as triacetin, cellulose based filter material such as paper, thermoplastic-based fibers, plugwrap, fiber-to-plugwrap adhesive, plugwrap hot-melt adhesive, and powderous additives such as activated carbon, silica gel, alumina, zeolites and combinations thereof.

The fibrous filter element comprising fibers of a polymeric material containing covalently bonded acetoacetyl residues (AcAc polymers) may be prepared by first reacting a polymer containing hydroxyl groups, e.g., a polymer having a hydroxyl number of at least 5, preferably about 25 to 180, with an alkyl acetoacetate or diketene. Acid and hydroxyl numbers are determined by titration and are reported herein as mg KOH consumed for each gram of polymer. Various methods for the preparation of acetoacetylated polyester coating resins have been described by Witzeman et al. in the Journal of Coatings Technology, Vol. 62, No. 789, pp. 101-112 (1990). Suitable alkyl acetoacetates for the reaction with (esterification of) a hydroxyl-containing polymer include t-butyl acetoacetate, ethyl acetoacetate, methyl acetoacetate, isobutyl acetoacetate, isopropyl acetoacetate, n-propyl acetoacetate, and n-butyl acetoacetate. t-Butyl acetoacetate is preferred. The AcAc polymer thus prepared may then be converted to fibers or a fibrous material by conventional techniques such as solution spinning, melt spinning and melt blowing. The fibers or fibrous materials may be formed into a tobacco smoke filter according to known means such as forming a tow of the fibers, blooming the tow and drawing the bloomed tow through a funnel device to a diameter of about 6 to 9 mm. An adhesive or bonding agent, depending upon the particular AcAc polymer employed, is added, e.g., by spraying or roll coating, to cause formation of a firm, rigid filter element. Tobacco smoke filter tow typically comprises 2,000 to 30,000 filaments having a total denier of about 15,000 to 50,000.

A particularly preferred embodiment of the present invention is a fibrous filter element comprising fibers of cellulose acetate wherein the cellulose acetate contains covalently bonded acetoacetyl residues. The AcAc modified cellulose acetate may be prepared by reacting a cellulose acetate containing hydroxyl groups with an ester of acetoacetic acid or diketene. The unmodified cellulose acetate has a degree of acetyl substitution of about 1.2 to 2.8 per anhydroglucose unit. Suitable cellulose acetate materials for acetoacetylation are described in U.S. Pat. Nos. 6,184,373, 5,913,311, and 5,863,652 and the references cited therein. Cellulose acetate polymers containing covalently bonded acetoacetyl residues may be prepared by means of procedures analogous to those described in U.S. Pat. Nos. 5,521,304 and 5,595,591. Fibers may be prepared from acetoacetylated cellulose acetate by known spinning techniques.

Fibers of cellulose acetate wherein the cellulose acetate contains covalently bonded acetoacetyl residues, i.e., cellulose acetate acetoacetate fibers, also may be prepared by acetoacetylating cellulose acetate fibers. For example, cellulose acetate tow, a bundle of filaments consisting of about 2,000 to 30,000 cellulose acetate fibers or filaments, may be contacted with diketene or an alkyl acetoacetate such as t-butyl acetoacetate in the presence of a diluent, i.e., a liquid that does not dissolve the cellulose acetate fibers or alter significantly the fiber structure, at a temperature of about 60 to 120° C. under anhydrous or substantially anhydrous conditions. The cellulose acetate of the cellulose acetate fibers typically has a degree of acetyl substitution of about 1.2 to 2.8 and more preferably 1.8 to 2.5 per anhydroglucose unit. Examples of suitable diluents include hydrocarbons such as toluene, benzene, xylene, and Aromatic 100, 150, or 200 available from ExxonMobile Chemical and supercritical carbon dioxide. The acetoacetylation may be promoted by including a catalyst in the reaction mixture. Examples of suitable catalysts include tertiary amines such as 4-(dimethylamino)pyridine (DMAP) and nicotine. The cellulose acetate acetoacetate thus prepared typically has an acetoacetyl degree of substitution of about 0.01 to 1, preferably about 0.01 to 0.3, per anhydroglucose unit. At the conclusion of the acetoacetylation reaction, the cellulose acetate acetoacetate fibers may be separated from the liquid reaction medium and washed with a liquid hydrocarbon to remove unreacted diketene or other acetoacetylating agent.

Cellulose acetate acetoacetate fibers may be prepared by acetoacetylating cellulose acetate fibers in the vapor phase. Such a vapor-phase acetoacetylation reaction represents another embodiment of the present invention for the preparation of a fibrous filter element comprising fibers of cellulose acetate wherein the cellulose acetate contains covalently bonded acetoacetyl residues which comprises contacting fibers of cellulose acetate containing hydroxyl groups with diketene or an alkyl acetoacetate. For example, cellulose acetate fibers, tow or a tobacco smoke filter formed from cellulose acetate fibers wherein the cellulose acetate contains hydroxyl groups, may be contacted with a vapor of diketene or other acetoacetylating agent, e.g., an alkyl acetoacetate such as t-butyl acetoacetate, at a temperature of about 20 to 180° C. at ambient or under reduced pressure. Acetoacetylation with diketene typically is carried out at a temperature of about 25 to 120° C., preferably at a temperature of about 40 to 100° C. The reaction of cellulose acetate with an alkyl acetoacetate to provide cellulose acetate acetoacetate typically is carried out at a temperature of about 40 to 180° C., preferably at a temperature of about 100 to 180° C. The cellulose acetate from which the cellulose acetate fibers are formed contains hydroxyl groups and has a degree of acetyl substitution of about 1.8 to 2.8 per anhydroglucose unit. Solid cellulose acetate fiber tow may be reacted with diketene in the vapor phase. Diketene may be vaporized by heating and/or using reduced pressure, e.g., pressure in the range of about 0.5 to 750 Torr. The gaseous diketene is then reacted with the cellulose fibers at ambient or elevated temperature. Optionally, a tertiary amine such as triethylamine, dimethylaminopyridine or nicotine may be used as a basic catalyst, for example, by applying nicotine onto cellulose acetate filter tow prior to the reaction with diketene. AcAc functional fibers thus prepared contain a nicotine residue, which can also function as a catalyst for reaction with aldehydes.

A non-volatile acetoacetic acid adduct such as glycerol triacetoacetate may be used to react with a cellulose acetate resin. In such a reaction, either a stoichiometric or an excess amount of the acetoacetic acid adduct is employed for the reaction. The unreacted acetoacetic acid adduct remaining in the cellulose acetate resin may function as a blend component or a plasticizer for the resulting acetoacetate-containing cellulose acetate resin or fibers to enhance its reactivity toward aldehydes.

The fibrous filter element comprising fibers of cellulose acetate wherein the cellulose acetate contains covalently bonded acetoacetyl residues preferably is a tobacco smoke filter. Tobacco smoke filters may be produced from a collection of cellulose acetate or cellulose acetate acetoacetate fibers referred to as filter tow. Tobacco smoke filter tow typically comprises 2,000 to 30,000 filaments having a total denier of about 15,000 to 50,000. The cellulose acetate fibers typically are produced by a dry spinning process such as those disclosed in U.S. Pat. Nos. 2,829,027 and 2,838,364. The cellulose acetate fibers may be dry spun from a cellulose acetate or cellulose acetate acetoacetate spinning solution containing cellulose acetate or cellulose acetate acetoacetate and acetone or other solvent with other optional additives such as titanium dioxide. The dry spinning process of producing the cellulose acetate fibers generally produces fibers having an average denier per filament (dpf) of about 2 to 8, but fibers can be made down to 1 and up to 20 dpf. The spinning process can produce various fiber cross sections, for example a triangular hole is used to form the Y cross section, the most common cross section. A cigarette typically consists of two parts—a smoke filter and a tobacco rod.

EXAMPLES

The preparation of the particulate filter media of the present invention and the use thereof to adsorb aldehydes are further illustrated by the following examples wherein all percentages are by weight unless specified otherwise.

Example 1 Preparation of Acetoacetate-Functional Cellulose Acetate Tow

A sample of cellulose acetate filter tow (25.2 g) was added to a 1 L, round-bottom flask equipped with a thermowell, a rod shaped magnetic stirring bar under argon, a vigereux column, and a distillation take off head. The cellulose acetate of the filter tow has an acetyl degree of substitution (DS) of 2.45 providing an expected free hydroxyl content of 52 millimoles (mmol). The filter tow consisted of cellulose acetate filaments having a denier per filament of 2.7 and a total denier of 35,000. To the flask was charged toluene (502.7 g) and the mixture was heated to reflux (pot temperature=109° C.) and maintained at reflux for 30 minutes. The resulting distillate (8 g) was removed until it was no longer cloudy; the distillate was found to contain about 1 ml of water. Over a 30 to 60 minute period the mixture was permitted to cool to 60° C. using a heating mantel as an insulator. 4-(Dimethylamino)pyridine (DMAP; 0.47 g) then was added and mechanically mixed in with a metal spatula (the magnetic stir bar was left in a vibrate mode at the lowest setting so as to not alter the structure of the tow and because the swelled tow prevented stirring).

Diketene (7.68 g, 91.3 mmoles, 1.7 equivalents relative to free hydroxyls) was added in 4 portions via pipette (subsurface addition in different locations) over 10 minutes. Obvious discoloration of the solution occurred at the addition points of the diketene. The final solution color was a clear red-brown. The reaction self heated from 60 to 63-64° C. A small amount of the filter tow rose out of the solution, and it was necessary periodically to push it back in with a metal spatula. The reaction mixture was gently agitated (stir bar in vibrate mode and approximately 4 manual stirrings with a spatula) and maintained at 60-64° C. for 5.5 hours. The mixture was allowed to cool overnight. The resulting tow (still containing fiber ribbon like character) was then filtered through a 2 L coarse fritted funnel, washed with 4×500 ml of toluene using gentle stirring (spatula) and gravity filtration over 1 hr to provide long contact time, and suction dried overnight. A 26.17 g amount of the fibrous tow product was obtained. The fiber character of the filter tow survived significantly. Except for several hard/yellow brown spots, the majority of the ribbon was of light yellow color with slight variation at different locations.

A 0.6 g samples of the acetoacetylated cellulose acetate fibrous material were taken from 3 locations using a pair of scissors. The first 2 samples (Samples A and B) were taken from the bulk fibrous material. The third sample (Sample C) was taken from one of the hard yellow-brown regions (a circular section of about 1 cm radius). The three samples were analyzed by proton NMR and determined to contain acetoacetate functionality in the amounts of DS 0.06 (Sample A), DS 0.04 (B) and DS 0.28 (C). (DS: degree of substitution based on 3 equivalents of hydroxyl groups in cellulose per anhydroglucose unit, e.g. fully acylated cellulose has a DS of 3 in acyl).

Example 2 Preparation of Acetoacetate-Functional Cellulose Acetate Tow

In this example a large excess of diketene was used to obtain a higher degree of acetoacetate substitution. The cellulose acetate of the filter tow utilized has an acetyl DS of 2.45 providing an expected free hydroxyl content of 53 mmol. Cellulose acetate filter tow (25.77 g) was added to a 1 L, round-bottom flask equipped with a thermowell, a glass mechanical stirrer under argon, a vigereux column, and a distillation take off head. The filter tow consisted of cellulose acetate filaments having a denier per filament of 2.7 and a total denier of 35,000. To the flask was charged toluene (503.00 g) and the mixture was heated to reflux (pot temperature=109° C.) and maintained at reflux for 30 minutes. The resulting distillate (5 g) was removed until it was no longer cloudy; the distillate was found to contain about 1 ml of water. Over a 30 to 60 minute period the mixture was permitted to cool to 60° C. using a heating mantel as an insulator.

DMAP (0.50 g) then was added and diketene (35.82 g, 426 mmoles, 8.04 equivalents per equivalent of free hydroxyl) was charged into an addition funnel. With manual mechanical stirring (glass mechanical stirring rod without Teflon blade), the diketene was added over 2 hours by careful dropwise addition to maintain the reaction temperature at about 60° C. Discoloration of the solution occurred at the points of the diketene addition. Care was taken to avoid direct contact of diketene drops with the tow. The reaction temperature was maintained at 57 to 62° C. during the period of the reaction (2 hours). After the reaction period the mixture was allowed to cool overnight. The resulting tow (still containing fiber-like character) then was filtered through a 2 L, coarse fritted funnel, washed with 4×700 ml of toluene using gentle stirring (spatula) and gravity filtration over 1 hour to provide long contact time, and suction dried overnight. The fiber character of the acetoacetylated, fibrous tow product (28.93 g) survived substantially. Except for several hard/brown spots, the majority of the filter tow ribbon was of yellow color (darker than that of Example 1) with slight variation at different locations. Because of interferences observed in the proton NMR, quantification for DS was by C13 NMR as described by Lowman, Characterization of cellulose esters by solution-state and solid-state NMR spectroscopy, Douglas W. Lowman, ACS Symposium Series (1988), 688 (Cellulose Derivatives), 131-162). A sample of the fiber tow produced had a C13 NMR measured acetoacetyl DS of 0.14 and acetyl DS of 2.44.

Example 3 Preparation of Acetoacetate-Functional Cellulose Acetate Filter Rod

This example illustrates the reaction of gaseous diketene with cellulose acetate in the form of a filter rod 12.5 cm in length having an outside diameter of 8 mm). The filter rod (approximately 0.8 g weight) is produced from cellulose acetate filter tow and paper wrap wherein the cellulose acetate of the filter tow utilized has an acetyl DS of 2.45 providing an expected free hydroxyl content of 1.7 mmol. The filter tow consisted of cellulose acetate filaments having a denier per filament of 2.7 and a total denier of 35,000. The filter rod was inserted tightly into a glass tube equipped with vacuum tubing and vacuum meters on both ends. To one end was attached a vacuum pump with trap filled with dry ice. To the other end was attached a 15-mL round-bottom vacuum flask charged with diketene (5.0 g). The pump then was turned on to yield a vacuum of about 3 mm-Hg on the pump side and 8 mm-Hg on the flask side. This apparatus allowed diketene to vaporize and enter the filter rod to react with cellulose acetate comprising the filter rod. The process was allowed to continue for 5 hours with no change in the color of the filter rod. The amount of diketene remaining in the flask after the reaction was 3.0 g. Thus, the total amount of diketene vapor passing through the filter rod was approximately 2 g (24 mmol). Proton NMR analysis showed only slight reaction occurred.

Example 4 Preparation of Acetoacetate-Functional Cellulose Acetate Filter Rods

This example illustrates the utilization of nicotine as a catalyst for the reaction of gaseous diketene with cellulose acetate according to the procedure described in Example 3. The filter rod was dipped into an aqueous solution of nicotine (approximately 1%) for about one minute and subsequently freeze-dried for about 24 hours. The resulting filter plug then was reacted with gaseous diketene as described in Example 3. During the reaction the filter plug gradually turned yellow. The coloration extended over about ¾ of the rod length from the flask side and was more distinct in the middle. The reaction was terminated after 5 hours and found to consume about 1 g liquid diketene (12 mmol). Proton NMR analysis showed the presence of acetoacetate groups in an amount that was approximately 2 times or more the level observed in Example 3. Interferences were seen in the proton NMR in the acetoacetyl methyl region (2.1-2.45 ppm) and acetyl methyl region (1.7-2.2 ppm) which made quantification of DS difficult and imprecise.

Example 5 Preparation of Acetoacetate-Functional Cellulose Acetate

This example illustrates the preparation of acetoacetyl functional cellulose acetate using a solution of cellulose acetate in acetone dope and diketene. To a 1-L, 3-neck, round-bottom flask equipped with magnetic stirrer, thermowell, and reflux condenser was added 495.52 g of a 5.75% solution of cellulose acetate in acetone. The cellulose acetate contained 51.5 mmol of free hydroxyl and the acetone solution contained 109 mmol of water. The stirred reaction mixture was heated to reflux (53-55° C.) under argon and subsequently allowed to cool to 40° C. At 40° C. DMAP (0.50 g) was added and the mixture brought back to reflux. Diketene (14.52 g, 172.7 mmol) was added gradually from an addition funnel at 48° C. A vigorous reflux was observed (53° C.) after half of the diketene was added. After the temperature dropped to 49° C., the remainder of the diketene was added dropwise. After the addition was complete, the mixture was analyzed by GC and found to contain neither dehydroacetic acid nor diketene. The resulting mixture then was added to 3 Kg methanol to give a white, fibrous precipitate which was subsequently isolated, washed with 2×500 ml methanol, and suction dried. The amount of the fibrous product obtained was 27.53 g. Carbon-13 NMR analysis showed the presence of acetoacetate groups in an acetoacetyl DS 0.18 and an acetyl DS of 2.36.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

1. A fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues.
 2. The fibrous filter element of claim 1 wherein the polymeric material is cellulose acetate having an acetyl degree of substitution of about 1.2 to 2.8.
 3. The fibrous filter element of claim 2 wherein the filter element is a tobacco smoke filter comprising 2,000 to 30,000 cellulose acetate filaments having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 50,000 and the cellulose acetate contains covalently bonded acetoacetyl residues
 4. A method of removing a gaseous aldehyde from tobacco smoke by contacting tobacco smoke containing one or more aldehydes with a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues.
 5. A method according to claim 4 wherein the polymeric material is cellulose acetate having an acetyl degree of substitution of about 1.2 to 2.8.
 6. A method according to claim 4 wherein the filter element is a tobacco smoke filter comprising 2,000 to 30,000 cellulose acetate filaments having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 50,000 and the cellulose acetate contains covalently bonded acetoacetyl residues
 7. A smoking article comprised of a first section comprising burnable tobacco and a second filter plug section comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues.
 8. A smoking article according to claim 7 wherein the polymeric material is cellulose acetate having an acetyl degree of substitution of about 1.2 to 2.8.
 9. A smoking article according to claim 7 wherein the filter plug comprises 2,000 to 30,000 cellulose acetate filaments having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 50,000 and the cellulose acetate contains covalently bonded acetoacetyl residues.
 10. A method for the preparation of a fibrous filter element comprising fibers of a polymeric material wherein the polymeric material contains covalently bonded acetoacetyl residues which comprises contacting a fibrous material constructed of or comprising a reactant polymer containing hydroxyl groups with gaseous diketene.
 11. A method according to claim 10 wherein a fibrous filter element comprising fibers of cellulose acetate having an acetyl degree of substitution of about 1.2 to 2.8 is contacted with gaseous diketene at a temperature of about 25 to 120° C.
 12. A method according to claim 10 wherein a fibrous filter element comprising fibers of cellulose acetate having an acetyl degree of substitution of about 1.8 to 2.5 is contacted with gaseous diketene at a temperature of about 40 to 100° C. in the presence of a catalytic amount of a tertiary amine.
 13. A method according to claim 11 wherein the fibrous material is a tobacco smoke filter element comprising 2,000 to 30,000 cellulose acetate filaments having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 50,000 and the cellulose acetate contains covalently bonded acetoacetyl residues.
 14. A method according to claim 11 wherein a tobacco smoke filter element comprising 2,000 to 30,000 cellulose acetate filaments having a denier per filament of about 2 to 8 and a total denier of about 15,000 to 50,000 is contacted with gaseous diketene at a temperature of about 40 to 100° C. in the presence of a catalytic amount of a tertiary amine, wherein the cellulose acetate has an acetyl degree of substitution of about 1.8 to 2.5. 